Dynamic covalent polymer networks via combined nitroxide exchange reaction and nitroxide mediated polymerization†
Although the control of chemical composition and macromolecular architectures of polymer networks is crucial to tailor their properties, the control and characterization of the crosslinking density and defects remains challenging. Therefore, new synthetic approaches are needed, which can, on the one hand dynamically tune the network structure and functionalization, and on the other hand facilitate characterization. The present study explores the combination of nitroxide exchange reaction (NER) and nitroxide mediated polymerization (NMP), in different sequences, to prepare structurally tailored and engineered macromolecular (STEM) networks with controlled strand lengths. The radical nature of the NER enables the precise monitoring of the reaction progress and determination of the defect ratio of the networks in a straightforward manner via electron paramagnetic resonance (EPR) spectroscopy. Additionally, the dynamic nature of the NER permits the disassembly of the networks and the determination of the strand length of the prepared networks by size exclusion chromatography (SEC). The final networks are also characterized by inverse size exclusion chromatography (ISEC) to determine and compare their mesh-size distributions. Thus, this study demonstrates that the combination of NER and NMP offers a versatile approach for the preparation of dynamic polymer networks with controlled and tunable structures.